In recent years, lasers and other solid-state light sources capable of producing visible light have drawn significant attention as alternative light sources to traditional light sources for use in imaging systems such as projection systems. This attention has been due to many advantages of these light sources, such as compact size, greater durability, longer operating life, higher efficiency, and lower power consumption.
Regardless of certain superior properties over traditional light sources, solid-state light sources may produce unwanted artificial effects, one of which is speckle effect. Speckle effect arises when phase-coherent light, such as light from solid-state illuminators is scattered from a rough surface, such as a rough surface of a screen on which the images are displayed using the coherent light, and the scattered coherent light is detected by a detector having a finite aperture, such as the viewer's eyes. An image displayed on the screen appears to comprise quantized areas with sizes around the size of the detector's aperture. The intensities of the quantized areas in the displayed image often vary randomly, and such intensity variation (or fluctuation) is often referred to as the speckle effect.
In display applications using coherent light, such as light from solid-state illuminators, speckles accompanying the desired image displayed on a screen overlap with the desired image, and thus may significantly degrade the quality of the displayed image.
Therefore, elimination or reduction of the speckle effect in display applications using phase-coherent light is highly desirable.